1. Field of Invention
This invention relates to torque rebalancing of inertial sensors, and more particularly to a dual range torque rebalance feedback loop control apparatus and output integrator for use with torque rebalanced inertial sensors.
2. Description of the Prior Art
As is known, low drift, substantially error-free operation of inertial sensors, such as accelerometers and gyros, is enhanced by pulse torque feedback which electromagnetically drives the output axis of the sensor in a direction opposite to the motion induced by the inertial phenomenon (acceleration or angular rate) being sensed thereby. The signal output of the sensor is utilized to control feedback current applied to the torque rebalancing magnet winding, such that the output signal is reduced to substantially zero, and a signal proportional to the applied feedback is used as an output indication of the magnitude of the inertial parameter being sensed. In pulse torque rebalanced inertial sensor apparatus, there are important trade-offs between the dynamic range, resolution and accuracy, especially in gyro sensor loops. For high rates, the torque rebalancing feedback current must be increased in order to balance the higher forces relating to higher rates; but resolution and accuracy vary, in part, in proportion with torque rebalancing feedback current. Thus, resolution and accuracy are decreased when the system is designed to operate at high rates. But if the torque rebalancing feedback current is kept relatively small for good accuracy and resolution, the sensor loop will saturate at correspondingly lower rates. Stated alternatively, an inertial sensor, particularly a gyro, which must sense both low rates and high rates suffers the consequences of the errors which are nominally related to full scale (high rates) even at low ends of the scale (low rates).
Another problem, particularly in space applications, is that the power consumption and the size and weight of the power supplies necessary to operate a torque rebalanced inertial sensor loop is directly proportional to the maximum rate which can be sensed thereby. If high angular rates or accelerations need be sensed during maneuvering, so that a high capacity is provided, then there is a large power consumption all of the time, even when only low rates are being sensed. On the other hand, if the power consumption is maintained at a low level so as to handle only the low angular rates or acceleration which are encountered most of the time, then the sensor will saturate and not provide correct outputs during high-rate maneuvering.